Senator Joe Manchin III has asked the U.S. Food and Drug Administration (FDA) to conduct a probe over so-called “pay to play” allegations concerning one of its advisory panels. The request came following news that pharmaceutical firms paid to attend meetings with a scientific panel that advised the FDA on painkillers. According to the organizer’s emails, key drug maker funding was as high as $25,000 per meeting, The Washington Post reported.

Senator Manchin (Democrat-West Virginia) wrote to FDA Commissioner Margaret Hamburg asking the agency to provide his office with a number of documents, including the names of the firms that paid to attend panel meetings, how much they paid, and the emails that passed between meeting organizers and FDA officials, The Washington Post reported. The senator seeks more stringent hydrocodone limits. Hydrocodone is a key ingredient in the painkillers Vicodin and Lortab, and is known for its addictive properties and its easy availability.

Drug firms and other groups have fought against the effort, arguing that the restrictions would make it more difficult for patients who need the drugs to get them, according to The Washington Post. “It is a shame that some of these companies were able to influence the FDA’s decision with a $25,000 contribution, while West Virginian families are destroyed by the addiction these pills cause,” Manchin said in a statement. The senator is also “calling for a full investigation to see how far this goes. If these allegations are true, they explain why it has taken the FDA almost a year to reach a decision to reschedule hydrocodone.”

Senator Manchin cited a Washington Post report published last week that discussed how drug firms paid up to $25,000 to attend the scientific panel’s meetings, according to emails that were sent among organizers. The panel was involved with safety and efficacy testing policies that were utilized by the agency and, according to the Washington Post report, were funded by drug makers, which allegedly paid hundreds of thousands of dollars. The report also indicated that hundreds of emails obtained by a public records request disclosed that drug makers paid about $25,000 to attend a meeting.

Two academics scheduled the meetings to provide the FDA with advice on how to measure evidence from clinical trial, according to the Washington Post; an agency official described the group as “an essential collaborative effort.” Consumer advocates have disagreed, saying that the FDA has become overly cozy with drug makers hoping to be part of the $9 billion United States pain killer market. Meanwhile, two officials later secured positions as consultants to the pharmaceutical industry. The FDA maintains it is “unaware of any improprieties.”

Robert Dworkin of the University of Rochester and Dennis Turk of the University of Washington organized the group; the emails generally involved the meetings’ financing and organizing, according to the Washington Post report. The professors received about $50,000 each per meeting, which they have said went to their academic research accounts, research assistant costs, expenses, “or to cover a small percentage of faculty effort,” they said. Emails also indicated that the pair issued a proposal for both to receive honoraria of $5,000 each for a four-hour hotel meeting that was conducted near FDA offices.